Fiber-optic communication devices typically use a transmit channel and a receive channel to allow communications with many of today's computer and electronic systems. The use of integrated circuits has allowed communication devices to be manufactured in smaller and smaller modules. Generally speaking, integrated circuits are very susceptible to electromagnetic noise and will not function properly if a large amount of noise is present near the integrated circuit. This is particularly noticeable in an integrated circuit with a receive channel. As such, care must be taken to ensure noise will not interfere with a fiber-optic communication module having both a transmitter and a receiver (transceiver).
In the past, a manufacturer, in order to ensure proper operation, designed a transceiver with two separate integrated circuit chips in the module. One integrated circuit was designed for the transmitter and one integrated circuit was designed for the receiver. Furthermore, each integrated circuit could be designed to have more than one transmitter or receiver on the chip, i.e., a multichannel device. Particularly problematic, however, was designing an integrated circuit with both a transmit channel and a receive channel on the same integrated circuit, i.e. a single die.
The common perception of the past was that a transmitter was too noisy to be included on the same integrated circuit as a noise-sensitive receiver. Consequently, most transceiver modules are able to accomplish an acceptable level of operation with only a transmitter and a receiver on two physically separate integrated circuits. An example of such a multichannel device is described in detail in A Si Bipolar Laser Diode Driver/Receiver Chip Set for 4-channel 5 Gb/s Parallel Optical Interconnection, Nagahori et al., ISSCC, Gigabit Optical Communications II Conference Journal, February 2001.
Furthermore, digital circuitry, such as clocked logic circuitry, was typically omitted from receiver circuits because as stated above receiver circuits are very sensitive to noise. Therefore, standalone receiver chips typically didn't have the functionality that digital circuitry offers.